Process for smoothing water-felted articles

ABSTRACT

A process for smoothing water-felted board, comprising passing the wet mat under a free-floating roller the diameter of which does not exceed about 1 inch.

United States Patent [1 1 lzard et al.

[ Sept. 23, 1975 1 PROCESS FOR SMOOTHING WATER-FELTED ARTICLES [75] Inventors: David G. lzard, Hoffman Estates;

Robert E. Fredericksen, McHenry,

21 Appl. No.: 430,001

[52] US. Cl. 162/204; 162/289; 162/361 [51] Int. Cl. D21F 11/00; D21H 5/06 [58] Field of Search 162/204, 205, 305, 361,

[56] References Cited UNITED STATES PATENTS 1,944,093 1/1934 Maggart 162/305 3,483,079 12/1969 Beachler 162/358 FORElGN PATENTS OR APPLICATIONS 157,276 10/1939 Germany 162/314 Primary Examiner-S. Leon Bashore Assistant Examiner-Peter Chin Attorney, Agent, or Firm-Samuel Kurlandsky, Esq.; Kenneth E. Roberts, Esq.; Stanton T. Hadley, Esq.

[57] ABSTRACT A process for smoothing water-felted board, comprising passing the wet mat under a free-floating roller the diameter of which does not exceed about 1 inch 3 Claims, 1 Drawing Figure PROCESS FOR SMOOTHING WATER-FELTED ARTICLES BACKGROUND OF THE INVENTION 1. Field of the Invention Board such as ceiling board, formboard, and insulation board is commonly manufactured on a Fourdrinier machine from an aggregate of mineral fibers, expanded perlite, clay, and a binder. The water-felting of such articles is a layering process which, after wet pressing, tends to produce an exterior surface that reflects the layers high points and low points. Ideally, however, a perfectly smooth, flat surface is desired. In ceiling board, except on specialized textured articles, smoothness is desired for appearance, while formboard and insulation board require smoothness if they are to be laminated to other materials. The invention thus provides a process for obtaining such a smooth, flat surface.

2. Description of the Prior Art Heretofore, attempts have been made to smooth the water-felted wet lap through the use of large pressure rollers, or by sanding and planing the dry surface. Thus, pressing or squeezing rollers have been used to remove surplus water prior to heating the sheet in a dryer, as shown in U.S. Pat. No. 2,030,625. Still others have attempted to smooth out the slurry in the headbox. An example of the use of pressure rollers is shown in U.S. Pat. No. 2,441 ,l69. All of these prior solutions, except for the pressure roller, have either been too variable in result, or expensive. The large pressure roller has suffered the obvious disadvantage of increasing the density of the product along with the smoothness of the surface. Since the density of the board must fall within a certain range as dictated by its end use, and since the densityis conventionally controlled by the press section of the waterfelting line, any further significant increase in density created by treatment of the surface for smoothness cannot be tolerated.

Other fields of endeavor have also used rollers of one type or another to treat a formed sheet. For example, in the paper-making industry, large diameter freefloating or swimming calender rolls are used to smooth the surface of the paper. However, these rolls must be of large size due to the extremely high speed at which paper machines operate. Their size makes them totally unsuited for use with the board prepared by the instant invention.

In the formation of batting, one series of matting rolls is often used after the fibers are accumulated, as shown, for example, in U.S. Pat. No. 1,442,793. However, one pass through a stack of rollers is insufficient to solve the problem described above, concerning the surface irregularities of the wet mat.

In still another field, the art of non-woven fibers has utilized rollers for surface treatment. One approach, for example, is to pass a water-laid, rubberimpregnated felt through a series of pressure rollers, each succeeding roller being applied at increased pressure, permitted by the reaction of the rubber. An example of such a practice is shown in U.S. Pat. No. 2,064,360. However, the increase in pressure applied by successive rollers would only serve to drastically alter the density of the board, if applied to theinstant invention.

Another non-woven technique passes the fibers through a series of fluted drafting rollers, and a single calender stack. One example is shown in U.S. Pat. No. 3,409,945. However, the drafting rolls crimp the fibers, and the calender rolls are mounted pressed together, rather than freefioating. Such treatment of the board mat of the instant invention would deface and deform it beyond usefulness.

Yet another non-woven technique concerns a bonding treatment wherein the sheet is. subjected to a gas to chemically bond individual fibers. In such a process, rollers are used to feed the' sheet, to keep it taut, and to seal the gas chamber. An example of such a process is shown in U.S. Pat. No. 3,676,244. However, the rollers, though dead weight in nature, are not truly freefloating as they are biased by their mounting guides towards the sheet, so as to effectively seal off the gas chamber. Such biased rollers lack the'flexibility necessary to provide no appreciable change in the density of the board mat.

SUMMARY OF THE INVENTION The invention relates to a process for smoothing the surface of a water-felted board without signficantly affecting the density of the board. More specifically, there is provided an improved process for making smooth, waterfelted fiberboard, including the steps of mixing a slurry of fibers, fleting the slurry upon a moving foraminous screen, dewatering the slurry upon the screen so as to form a wet mat of fibers, and drying the mat to form a board-like product; the improvement comprising prior to said drying step, repeatedly contacting successive transverse portions of one surface of the wet mat with a free-floating roller having a diameter no greater than about one inch, whereby the surface of the mat is rendered smooth without materially increasing the density of the mat.

Accordingly, it is an object of the invention to produce a low density, smooth surface, water-felted board in an inexpensive, reproducible manner.

It is a related object of the invention to provide such a process without adversely affecting the density of the board.

Other objects and advantages will become apparent upon reference to the following brief description of the drawing and the detailed discussion of the invention.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE is a partially schematic illustration of the invention, showing in transverse cross section a first pass of the wet mat under the free-floating roller.

DESCRIPTION OF THE PREFERRED EMBODIMENTS This disclosure concerns a process for smoothing the wet mat of a continuous water-felted mineral fiber line, prior to the drying of the mat and its complete processing into board such as ceiling board, insulation board, formboard, etc. Mineral fibers, as used in this application, means inorganic fibers selected from slag wool, glass fibers which are spun or drawn, asbestos, steel wool and rock wool. By slag wool, it is meant any bunched amorphous elongated filaments having been made predominantly from iron, copper, or lead blast furnace slag, and having a composition comprising silicon dioxide and metallic oxides, the percentage by weight of the metallic oxides being greater in total than the percentage of silicon dioxide.

The apparatus used to form the wet mat is conventional Fourdrinier equipment, so that a detailed description thereof is unnecessary. Briefly, however; a slurry of 2-671- consistency is prepared by mixing mineral fibers with other conventional ingredients. noted above. From the headbox, the slurry is deposited or felted upon the moving foraminous screen, and carried through the press section where vacuum boxes and pressure rollers continue the dewatering process that began upon the casting of the slurry. The pressure rollers also deform the mat so as to approach the final-desired density, namely between about 13 to about 30 pounds per cubic feet. The actual value depends upon the particular board being made.

After leaving the press section, the wet mat still has a water contact in the range of about 60 to 7071 by weight,-and it has the appearance shown on the lefthand side of the mat in FIG. 1, identified as portion 12. That is, after the press section the mat portion 12 has a wavy surface 14, exaggerated here for clarity, caused by the depositing of the solids in transversely extending ridges l6. 7

In accordance with one aspect of the invention, the wet mat is at this point passed under a free-floating roller having specific characteristics. The under surface of the wet lap is supported by any conventional means, here shown as a support roller 22. Side rails 24 provided with vertical slots 26 may be used, for example, to permit the roller 20 to float in its position directly aboveroller 22. Alternatively, a pair of rollers 20 may be mounted above roller-22 but spaced equidistant from a vertical plane passed through roller 22. Also a conveyor belt may be used in place of roller 22. I

In any event, it has been discovered that such a roller 20, if small enough in size, will act to knead the surface 14 so as to redistribute the surface materials and to level out ridges 16, as it rotates. The wet mat, which may have a thickness between about 0.4 to about 1.5 inches, has sufficient spring-back under such conditions that the over-all thickness of portion 27 of the mat as it exits from the roller, and therefore the density of the mat, is not appreciably altered. The resulting surface 28 of portion 27 is greatly reduced in irregularities, as shown. I

However, if roller 20 exceeds a certain size, its surface becomes flatter and its weight greater to the point that it will not just sink into the mat and knead the surface. Instead, it compresses the mat permanently and overcomes the spring-back capability of the mat, thus undesirably increasing the density. Smoothness may be achieved, but at the expense of an increase in density. It has been found that the diameter of roller 20 must not exceed about one inch, or the above noted condition sets in. Even a one-inch roller produces a very slight increase in density. This increase, however, can be accommodated in the wet press section, due to its slight magnitude.

Roller 20 may be as small as one-eighth of an inch in diameter. If made out of mild steel rods, the following sized rollers have been found to be usable to deliver an approximate lineal pressure of the indicated magnitude.

Diameter (Inches) Pressure (Pounds/Ft.)

" Continued" Y I Roller 20 is shown as being mounted skew rather than transverse to the longitudinal axis of the mat. The purpose is to further insure a leveling of transverse ridges 16. However, a perfectly transverse alignment of roller 20 may also be used.

As shown, surface 28 of portion 27 of the mat retains a few irregularities after a single pass under roller 20. Therefore, another aspect of the invention is to repeatedly pass each-transverse portion of the mat under such a roller until the desired smoothness is achieved. Tests have shown that, after 20 such passes, no appreciable improvement is obtained from additional passes. The preferred number is from 15 to 20. The preferred manner of achieving this number of passes is to send the mat through once, a plurality of such roller stands 20 and 22 successively mounted in rails 24. All of such rollers 20 (not shown) will of course be free-floated, and preferably they have the same diameter. In contrast, rollers 22 may have a diameter as large as three inches. Alternatively, the same mat can be passed under a single roller stand comprising rollers 20 and 22, the desired number of times.

Subsequent to the smoothing process described above, the mat is dried and further processed in a conventional manner.

Although the invention has been described in connection with certain preferred embodiments, it is not limited thereto. For example, the roller 20 may be formed from other metals, and thus deliver a different pressure than is characteristic 'of mild steel. However, in no event should the diameter size limitation of about one inch be exceeded. Thus, it is intended that the invention cover all alternative arrangements, equivalents, and embodiments as may be included within the scope of the following claims.

What is claimed is: i 1. In a process for making smooth water-felted fiberboard, including the steps of g mixing a slurry of fibers, felting the slurry upon a moving foraminous screen, dewatering the slurry upon the screen so as to form a wet mat of fibers, and drying the mat to form a board-like product;

the improvement comprising, prior to said drying step, repeatedly contacting successive transverse portions of a surface of the wet mat with a freefloating substantially solid metal roller having a diameter no greater than about 1 inch,

whereby the surface of the mat is rendered smooth without materially increasing the density of the mat.

2. The improvement in the process of claim I, wherein said surface of the wet mat is contacted by a plurality of successively-mounted free-floating rollers having a diameter no greater than about one inch.

3. The improved process as defined in claim 2,.

wherein said rollers are mounted skew to the direction of travel of the mat and to a direction transverse to said travel direction. 

1. IN A PROCESS FOR MAKING SMOOTH WATER-FELTED FIBERBOARD INCLUDING THE STEPS OF MIXING A SLURRY OF FIBERS, FELTING UPON A MOVING FORAMINOUS SCREEN, DEWATERING THE SLURRY UPON THE SCREEN SO AS TO FORM A WET MAT OF FIBERS, AND DRYING THE MAT TO FORM A BOARD-LIKE PRODUCT, THE IMPROVEMENT COMPRISING, PRIOR TO SAID DRYING STEP, REPEATEDLY CONTACTING SUCCESSIVE TRANSVERSE PORTIONS OF A SURFACE OF THE SET MAT WITH A FREE- FLOATING SUBSTANTIALLY SOLID METAL ROLLER HAVING A DIAMETER NO GREATER THAN ABOUT 1 INCH, WHEREBY THE SURFACE OF THE MAT IS RENDERED SMOOTH WITHOUT MATERALLY INCREASING THE THE DENSITY OF THE MAT.
 2. The improvement in the process of claim 1, wherein said surface of the wet mat is contacted by a plurality of successively-mounted free-floating rollers having a diameter no greater than about one inch.
 3. The improved process as defined in claim 2, wherein said rollers are mounted skew to the direction of travel of the mat and to a direction transverse to said travel direction. 